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// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_HANDLES_GLOBAL_HANDLES_H_
#define V8_HANDLES_GLOBAL_HANDLES_H_
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
#include "include/v8-callbacks.h"
#include "include/v8-persistent-handle.h"
#include "include/v8-profiler.h"
#include "src/handles/handles.h"
#include "src/heap/heap.h"
#include "src/objects/heap-object.h"
#include "src/objects/objects.h"
#include "src/utils/utils.h"
namespace v8 {
namespace internal {
class HeapStats;
class RootVisitor;
// Global handles hold handles that are independent of stack-state and can have
// callbacks and finalizers attached to them.
class V8_EXPORT_PRIVATE GlobalHandles final {
public:
GlobalHandles(const GlobalHandles&) = delete;
GlobalHandles& operator=(const GlobalHandles&) = delete;
template <class NodeType>
class NodeBlock;
//
// API for regular handles.
//
static void MoveGlobal(Address** from, Address** to);
static Handle<Object> CopyGlobal(Address* location);
static void Destroy(Address* location);
// Make the global handle weak and set the callback parameter for the
// handle. When the garbage collector recognizes that only weak global
// handles point to an object the callback function is invoked (for each
// handle) with the handle and corresponding parameter as arguments. By
// default the handle still contains a pointer to the object that is being
// collected. For this reason the object is not collected until the next
// GC. For a phantom weak handle the handle is cleared (set to a Smi)
// before the callback is invoked, but the handle can still be identified
// in the callback by using the location() of the handle.
static void MakeWeak(Address* location, void* parameter,
WeakCallbackInfo<void>::Callback weak_callback,
v8::WeakCallbackType type);
static void MakeWeak(Address** location_addr);
static void AnnotateStrongRetainer(Address* location, const char* label);
// Clear the weakness of a global handle.
static void* ClearWeakness(Address* location);
// Tells whether global handle is weak.
static bool IsWeak(Address* location);
explicit GlobalHandles(Isolate* isolate);
~GlobalHandles();
// Creates a new global handle that is alive until Destroy is called.
Handle<Object> Create(Tagged<Object> value);
Handle<Object> Create(Address value);
template <typename T>
inline Handle<T> Create(Tagged<T> value);
void RecordStats(HeapStats* stats);
size_t InvokeFirstPassWeakCallbacks();
void InvokeSecondPassPhantomCallbacks();
// Schedule or invoke second pass weak callbacks.
void PostGarbageCollectionProcessing(v8::GCCallbackFlags gc_callback_flags);
void IterateStrongRoots(RootVisitor* v);
void IterateWeakRoots(RootVisitor* v);
void IterateAllRoots(RootVisitor* v);
void IterateAllYoungRoots(RootVisitor* v);
// Marks handles that are phantom or have callbacks based on the predicate
// |should_reset_handle| as pending.
void IterateWeakRootsForPhantomHandles(
WeakSlotCallbackWithHeap should_reset_handle);
// Note: The following *Young* methods are used for the Scavenger to
// identify and process handles in the young generation. The set of young
// handles is complete but the methods may encounter handles that are
// already in old space.
// Iterates over strong and dependent handles. See the note above.
void IterateYoungStrongAndDependentRoots(RootVisitor* v);
// Processes all young weak objects:
// - Weak objects for which `should_reset_handle()` returns true are reset;
// - Others are passed to `v` iff `v` is not null.
void ProcessWeakYoungObjects(RootVisitor* v,
WeakSlotCallbackWithHeap should_reset_handle);
// Updates the list of young nodes that is maintained separately.
void UpdateListOfYoungNodes();
// Clears the list of young nodes, assuming that the young generation is
// empty.
void ClearListOfYoungNodes();
Isolate* isolate() const { return isolate_; }
size_t TotalSize() const;
size_t UsedSize() const;
// Number of global handles.
size_t handles_count() const;
size_t last_gc_custom_callbacks() const { return last_gc_custom_callbacks_; }
void IterateAllRootsForTesting(v8::PersistentHandleVisitor* v);
#ifdef DEBUG
void PrintStats();
void Print();
#endif // DEBUG
bool HasYoung() const { return !young_nodes_.empty(); }
private:
// Internal node structures.
class Node;
template <class BlockType>
class NodeIterator;
template <class NodeType>
class NodeSpace;
class PendingPhantomCallback;
void ApplyPersistentHandleVisitor(v8::PersistentHandleVisitor* visitor,
Node* node);
// Clears a weak `node` for which `should_reset_node()` returns true.
//
// Returns false if a node is weak and alive which requires further
// processing, and true in all other cases (e.g. also strong nodes).
bool ResetWeakNodeIfDead(Node* node,
WeakSlotCallbackWithHeap should_reset_node);
Isolate* const isolate_;
std::unique_ptr<NodeSpace<Node>> regular_nodes_;
// Contains all nodes holding young objects. Note: when the list
// is accessed, some of the objects may have been promoted already.
std::vector<Node*> young_nodes_;
std::vector<std::pair<Node*, PendingPhantomCallback>>
pending_phantom_callbacks_;
std::vector<PendingPhantomCallback> second_pass_callbacks_;
bool second_pass_callbacks_task_posted_ = false;
size_t last_gc_custom_callbacks_ = 0;
};
class GlobalHandles::PendingPhantomCallback final {
public:
using Data = v8::WeakCallbackInfo<void>;
enum InvocationType { kFirstPass, kSecondPass };
PendingPhantomCallback(
Data::Callback callback, void* parameter,
void* embedder_fields[v8::kEmbedderFieldsInWeakCallback])
: callback_(callback), parameter_(parameter) {
for (int i = 0; i < v8::kEmbedderFieldsInWeakCallback; ++i) {
embedder_fields_[i] = embedder_fields[i];
}
}
void Invoke(Isolate* isolate, InvocationType type);
Data::Callback callback() const { return callback_; }
private:
Data::Callback callback_;
void* parameter_;
void* embedder_fields_[v8::kEmbedderFieldsInWeakCallback];
};
class EternalHandles final {
public:
EternalHandles() = default;
~EternalHandles();
EternalHandles(const EternalHandles&) = delete;
EternalHandles& operator=(const EternalHandles&) = delete;
// Create an EternalHandle, overwriting the index.
V8_EXPORT_PRIVATE void Create(Isolate* isolate, Tagged<Object> object,
int* index);
// Grab the handle for an existing EternalHandle.
inline Handle<Object> Get(int index) {
return Handle<Object>(GetLocation(index));
}
// Iterates over all handles.
void IterateAllRoots(RootVisitor* visitor);
// Iterates over all handles which might be in the young generation.
void IterateYoungRoots(RootVisitor* visitor);
// Rebuilds new space list.
void PostGarbageCollectionProcessing();
size_t handles_count() const { return size_; }
private:
static const int kInvalidIndex = -1;
static const int kShift = 8;
static const int kSize = 1 << kShift;
static const int kMask = 0xff;
// Gets the slot for an index. This returns an Address* rather than an
// ObjectSlot in order to avoid #including slots.h in this header file.
inline Address* GetLocation(int index) {
DCHECK(index >= 0 && index < size_);
return &blocks_[index >> kShift][index & kMask];
}
int size_ = 0;
std::vector<Address*> blocks_;
std::vector<int> young_node_indices_;
};
// A vector of global Handles which automatically manages the backing of those
// Handles as a vector of strong-rooted addresses. Handles returned by the
// vector are valid as long as they are present in the vector.
template <typename T>
class GlobalHandleVector {
public:
class Iterator {
public:
explicit Iterator(
std::vector<Address, StrongRootBlockAllocator>::iterator it)
: it_(it) {}
Iterator& operator++() {
++it_;
return *this;
}
Handle<T> operator*() { return Handle<T>(&*it_); }
bool operator==(const Iterator& that) const { return it_ == that.it_; }
bool operator!=(const Iterator& that) const { return it_ != that.it_; }
Tagged<T> raw() { return T::cast(Tagged<Object>(*it_)); }
private:
std::vector<Address, StrongRootBlockAllocator>::iterator it_;
};
explicit inline GlobalHandleVector(Heap* heap);
// Usage with LocalHeap is safe.
explicit inline GlobalHandleVector(LocalHeap* local_heap);
Handle<T> operator[](size_t i) { return Handle<T>(&locations_[i]); }
size_t size() const { return locations_.size(); }
bool empty() const { return locations_.empty(); }
void Push(Tagged<T> val) { locations_.push_back(val.ptr()); }
// Handles into the GlobalHandleVector become invalid when they are removed,
// so "pop" returns a raw object rather than a handle.
inline Tagged<T> Pop();
Iterator begin() { return Iterator(locations_.begin()); }
Iterator end() { return Iterator(locations_.end()); }
private:
std::vector<Address, StrongRootBlockAllocator> locations_;
};
} // namespace internal
} // namespace v8
#endif // V8_HANDLES_GLOBAL_HANDLES_H_
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